TiNF and Related Analogues of TiO₂: A Combined Experimental and Theoretical Study

Abstract

Aliovalent anion substitution in inorganic materials brings about marked changes in properties, as exemplified by N,F‐codoped metal oxides. Recently, complete substitution of oxygen in ZnO by N and F was carried out to generate Zn2NF. In view of the important properties of TiO2, we have attempted to prepare TiNF by employing an entirely new procedure involving the reaction of TiN with TiF4. While the reaction at low temperature (450 °C) yields TiNF in the anatase phase, reaction at a higher temperature (600 °C) yields TiNF in the rutile phase. This is interesting since the anatase phase of TiO2 also transforms to the rutile phase on heating. The lattice parameters of TiNF are close to those of the parent oxide. Partial substitution of oxygen in TiO2 by N and F reduces the band gap, but complete substitution increases the value comparable to that of the oxide. We have examined properties of N,F‐codoped TiO2, and more interestingly N,F‐codoped Ti3O5, both with lower band gaps than the parent oxides. A detailed first‐principles calculations has been carried out on structural and electronic properties of N,F−TiO2 and the TiNF phases. This has enabled us to understand the effects of N,F substitution in TiO2 in terms of the crystal structure, electronic structure and optical properties.

Hg2NF, Analogue of HgO

“…The band widths of p orbitals of N and F at the top of valence band are 1.33 eV and 1.31 eV respectively. Earlier studies showed the VBM of TiNF and Cd 2 NF consists primarily of N‐2 p states and F‐2 p states lie around –2 eV with respect to VBM , . The p orbitals of N at the top of valence band has a band width of 0.68 eV in TiNF which is small compared to that in Hg 2 NF.…”

“…Materials such as Ca 2 NF, Sr 2 NF and Ba 2 NF have been reported, but the consequences of chemical ordering of N 3– and F – on the anion sublattice, structure and electronic properties have not been addressed . We have examined the change in the band gap with the substitution of N 3– and F – in ZnO and TiO 2 wherein the materials become colored and allow visible light excitation , . Substitution of sulfide anion in place of the oxide anion does not have such significant effects .…”

An Experimental Study of Carbon-Doped GaN via Solid–Gas Reaction Route and Investigation of Its Defect-Related Luminescence

“…Aliovalent anion substitution in oxides and sulfides such as TiO 2 , ZnO, CdO, and CdS has already been shown to modify the band structure and electronic properties of these materials, making them suitable for catalysis applications . Anionic substitution by a simple solid-state synthesis, O by N and F in TiO 2 (e.g., TiNF), , ZnO (e.g., Zn 2 NF), and CdO (e.g., Cd 2 NF) and sulfur­(S) by phosphorus (P) and chlorine (Cl) in CdS (e.g., Cd 2 PCl) gives rise to novel properties. Substitution changes the electronic structure and optical properties of the materials; therefore, this strategy would be interesting for the GaN to substitute C in place of N in the presence of O impurity.…”